The sulfur in a 5.00 g sample of steel was evolved as H 2 S and then collected i

Question

The sulfur in a 5.00 g sample of steel was evolved as H2S and then collected in a solution of CdCl2 to produce the precipitate CdS. The CdS was then titrated with excess I2 and the remaining I2 was then back titrated with 4.82 ml of 0.0510 M sodium thiosulfate. If the concentration of the I2 is 0.0600 M and a total of 10.0 ml is added, calculate the %S in the steel.

The relevant reactions are:
Titration (excess I2) -->  CdS + I2 ? S + Cd2+ + 2I-

Back Titration--> I2 + 2S2O32- ? S2O62- + 2I-

Explanation / Answer

The sulfur in a 5.00 g sample of steel was evolved as H2S and then collected in a
solution of CdCl2 to produce the precipitate CdS. The CdS was then titrated with excess
I2 and the remaining I2 was then back titrated with 4.82 mL of 0.0510 M sodium
thiosulfate. If the concentration of the I2 is 0.0600 M and a total of 10.0 mL is added,
calculate the %S in the steel. The relevant reactions are:
H2+S =H2S
CdS + I2 -> S + Cd2+ + 2I- Titration (excess I2)
I2 + 2(S2O3)2- -> (S2O6)2- + 2I- Back titration

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